Method for imparting annular oppositely polarized magnetically conditioned regions to a disk shaped member

ABSTRACT

A magnetic torque sensing device having a disk-shaped member with a magnetoelastically active region. The magnetoelastically active region has oppositely polarized magnetically conditioned regions with initial directions of magnetization that are perpendicular to the sensitive directions of magnetic field sensor pairs placed proximate to the magnetically active region. Magnetic field sensors are specially positioned in relation to the disk-shaped member to accurately measure torque while providing improved RSU performance and reducing the detrimental effects of compassing.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of U.S. Pat. No. 8,424,393,filed Oct. 18, 2011, the entire disclosure of which is incorporated byreference herein.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to methods and sensing devices forautomotive transmissions and, more particularly, to non-contactingmagnetoelastic torque sensors for providing a measure of the torquetransmitted radially in a transmission converter drive plate or similardisk-shaped member.

2. Description of the Related Art

In the control of systems having rotating drive shafts, torque and speedare fundamental parameters of interest. Therefore, the sensing andmeasurement of torque in an accurate, reliable, and inexpensive mannerhas long been a primary objective of such control system designs.

Previously, torque measurement was accomplished using contact-typesensors directly attached to a shaft. One such sensor is a “straingauge” type torque detection apparatus, in which one or more straingauges are directly attached to the outer peripheral surface of theshaft and a change in resistance caused by torque-induced strain ismeasured by a bridge circuit or other well known means. However,contact-type sensors are relatively unstable and of limited reliabilitydue to the direct contact with the rotating shaft. In addition, they areexpensive and are thus commercially impractical for competitive use inmany applications, such as automotive steering systems, for which torquesensors are sought.

Subsequently, non-contact torque sensors of the magnetostrictive typewere developed for use with rotating shafts. For example, U.S. Pat. No.4,896,544 to Garshelis, which is incorporated herein by reference,discloses a sensor comprising a torque-carrying member, with anappropriately ferromagnetic and magnetostrictive surface, two axiallydistinct circumferential bands within the member that are endowed withrespectively symmetrical, helically-directed residual stress-inducedmagnetic anisotropy, and a magnetic discriminator device for detecting,without contacting the torqued member, differences in the response ofthe two bands to forces applied to the torque-carrying member. Mosttypically, magnetization and sensing are accomplished by providing apair of excitation or magnetizing coils overlying and surrounding thebands, with the coils connected in series and driven by alternatingcurrent. Torque is sensed using a pair of oppositely connected sensingcoils for measuring a difference signal resulting from the externalmagnetic fluxes of the two bands. Unfortunately, providing sufficientspace for the requisite excitation and sensing coils on and around thedevice on which the sensor is used can create practical problems inapplications where space is at a premium. Also, such sensors may beimpractically expensive for use on highly cost-competitive devices, suchas in automotive applications.

Torque transducers based on measuring the field arising from the torqueinduced tilting of initially circumferential remanent magnetizationshave been developed which, preferably, utilize a thin wall ring(“collar”) serving as the field generating element. See, for example,U.S. Pat. Nos. 5,351,555 and 5,520,059 to Garshelis, which areincorporated herein by reference. Tensile “hoop” stress in the ring,associated with the means of its attachment to the shaft carrying thetorque being measured establishes a dominant, circumferentiallydirected, uniaxial anisotropy. Upon the application of torsional stressto the shaft, the magnetization reorients and becomes increasinglyhelical as torsional stress increases. The helical magnetizationresulting from torsion has both a radial component and an axialcomponent, the magnitude of the axial component depending entirely onthe degree of torsion. One or more magnetic field vector sensors may beused to sense the magnitude and polarity of the field arising, as aresult of the applied torque, in the space above the magneticallyconditioned regions on a shaft, and provide a signal output reflectingthe magnitude and direction of the torque. Inasmuch as the peakallowable torque in a ring sensor is limited by slippage at thering/shaft interface, concerns have been expressed regarding distortionarising from slippage at the ring/shaft interface under conditions oftorque overload. This, together with the need for multiple parts ofdifferent materials to minimize the adverse effects of parasitic fields,has encouraged the investigation of alternative constructions.

Magnetoelastic torque transducers have been developed in which theactive, torque sensing region is formed directly on the shaft itself,rather than on a separate ferromagnetic element which then has to beaffixed to the shaft. See, for example, U.S. Pat. No. 6,047,605 toGarshelis, which is incorporated herein by reference. In one form ofthese so-called “collarless” transducers, the magnetoelastically activeregion is polarized in a single circumferential direction and itselfpossesses sufficient magnetic anisotropy to return the magnetization inthe region, following the application of torque to the member, to thesingle circumferential direction when the applied torque is reduced tozero. The torqued shaft is desirably formed of a polycrystallinematerial wherein at least 50% of the distribution of localmagnetizations lie within a 90-degree quadrant symmetrically disposedaround the direction of magnetic polarization and have a coercivitysufficiently high that the transducing region field does not createparasitic magnetic fields in proximate regions of the shaft ofsufficient strength to destroy the usefulness, for torque sensingpurposes, of the net magnetic field seen by the magnetic field sensor.In particularly preferred forms of such transducers the shaft is formedof a randomly oriented, polycrystalline material having cubic symmetryand the coercivity is greater than 15 Oersted (Oe), desirably greaterthan 20 Oe and, preferably, greater than 35 Oe.

More recently, non-contacting magnetoelastic torque sensors have beendeveloped that provide signals indicative of the torque transmittedbetween radially separated locations of disk-shaped members. U.S. Pat.No. 6,513,395 to Jones, which is incorporated herein by reference,describes a torque sensor that includes a disk-shaped member having amagnetoelastically active region that is polarized in a singlecircumferential direction. In that patent, a magnetic field sensor ismounted proximate to the active region, the sensor sensing the magnitudeof a magnetic field resulting from a torque transferred from a shaft tothe disk-shaped member, and the sensor outputting a signal in responsethereto. Such a configuration may be susceptible to compassing asdiscussed below. That patent also describes a disk having dualcircumferentially and oppositely polarized regions, with two sensorspositioned along the same radial line, their sensitive directionsoriented radially and oppositely to permit common mode fieldcancellation. This placement of sensors, however, has the undesiredresult in which the sensors pick up magnetic field signals that do notchange linearly in response to a change in torque applied to the disk.

Other prior art describes a torque sensor that includes a disk-shapedmember having a region in which annular magnetically conditioned regionsare separated from one another and spaced in a radial direction. It isbelieved, however, that a torque sensor having a gap betweenmagnetically conditioned regions may exhibit a large rotational signaluniformity (RSU) signal due to random magnetic leakage fields betweenthe two annular magnetically conditioned regions. Ideally, a torquesensor will exhibit a zero RSU signal, which is defined as no variationin signal output during the rotation of a member when no torque, or aconstant torque, is applied to the rotating member. In actual practicehowever, due to deficiencies in the surface preparation andmagnetization processes, noticeable RSU signals are detected.Furthermore, a torque sensor having a disk-shaped member with a gapbetween magnetically conditioned regions requires additional space,which is not desirable in applications in which the disk has a limitedamount of flat surface available for magnetically conditioned regions.

Because magnetic fields, in the context of their measurement, arefungible, the sensors taught by the above and other prior art may besusceptible to other magnetic fields of exterior origin. In particular,the earth's magnetic field will cause a phenomenon known as“compassing,” in which the measured field is the sum of the torqueinduced magnetic field and the earth's magnetic field. Within thecontext of this disclosure, the term “compassing” shall be used todescribe any error resulting from the earth's magnetic field.

Magnetic fields of external origin can emanate from both far field andnear field sources. A far field source, such as the earth with itsmagnetic field, generally has the same effect on each magnetic fieldsensor in a torque sensing device having multiple magnetic fieldsensors. Near field sources, such as permanent magnets, magnetizedwrenches, motors, solenoids, etc., may create magnetic fields havingsignificant local gradients, thus having significantly different effectson the different magnetic field sensors in a torque sensing devicehaving multiple magnetic field sensors.

U.S. Pat. No. 5,520,059 to Garshelis addresses the compassing issue withrespect to far field sources. In that patent, a shaft is describedhaving two axially distinct magnetoelastically active regions, polarizedin opposite circumferential directions, with magnetic field sensorshaving opposite axial polarities positioned proximate to the activeregions and providing output signals in response to a torque applied tothe shaft. By summing the outputs of the magnetic field sensors, allcommon mode external magnetic fields, i.e. far fields, are canceled. Inapplications employing such a scheme, the oppositely polarized sensorsshould be placed as close to each other as possible to preserve theefficiency of the common mode rejection scheme. Sensors that are spacedfrom one another exhibit reduced common mode rejection efficiency, asthe earth's magnetic field may be significantly distorted aroundferromagnetic parts in and around the torque sensor.

U.S. Pat. App. Pub. No. 2009/0230953 to Lee, which is incorporatedherein by reference, describes a torque sensing device designed tocancel near field magnetic noise from external sources without cancelinga torque-induced magnetic field. That reference describes a torquesensor including three sets of magnetic field sensors, axially spacedproximate to a shaft, the shaft having a magnetoelastically activeregion that is polarized in a circumferential direction. Signalsreceived by each of the magnetic field sensors are adjusted tocompensate for the effects of near field sources.

In torque sensing devices having ferromagnetic members with annularmagnetoelastically active regions, it is desirable for a magnetic fieldsensor placed proximate to the magnetoelastically active region to pickup a signal that accurately represents the torque applied to the member,regardless of the angular distance between the magnetic field sensor anda radius of the member. Torque sensing devices that demonstrate thischaracteristic are said to demonstrate improved rotational signaluniformity (RSU). Non-uniformities in the depth, width, or magneticfield strength, about an annular magnetoelastically active region maylead to noticeable RSU signals and, hence, inaccurate torquemeasurements. Improved RSU performance, and a decreased hysteresiseffect, may also be achieved by subjecting the ferromagnetic member toan appropriate surface hardness process, as is known in the art, priorto magnetization. Lee, for example describes a torque sensing devicedesigned to exhibit improved RSU performance by incorporating aplurality of angularly and axially spaced magnetic field sensors placedproximate to a circumferential surface of a rotatable shaft.

The torque sensing devices described in the prior art are not speciallyconfigured for measuring the torque transmitted between a shaft and aradially separated portion of a disk-shaped member, while demonstratingimproved RSU performance and reducing detrimental effects caused bycompassing. Accordingly, there exists a need for such a device.

SUMMARY OF THE INVENTION

The present invention, as described herein, is generally applicable tothe measurement of torque in any disk-shaped member that is rotatableabout an axis, such as a pulley, gear, sprocket, or the like.

It is a principal object of the present invention to provide a torquesensing device having non-contacting magnetic field sensors positionedproximate to a disk-shaped member, for measuring the torque transmittedbetween a shaft and a radially separated portion of the disk-shapedmember.

It is another object of the invention to provide a torque sensing devicehaving magnetic field sensors that output a signal representative of anapplied torque, wherein the output signal varies linearly with respectto variations in the applied torque.

It is another object of the present invention to provide a torquesensing device having magnetic field sensors placed in pairs, themagnetic field sensors having their sensing directions opposite oneanother, to minimize the detrimental effects of magnetic noise,including compassing.

It is another object of the present invention to provide a torquesensing device with an annular magnetoelastically active region, havingdual, non-separated, oppositely polarized magnetically conditionedregions to enhance the RSU performance of the torque sensing device.

It is another object of the present invention to provide a torquesensing device with multiple, angularly-spaced magnetic field sensorsthat are specially positioned to enhance the RSU performance of thetorque sensing device.

Briefly described, those and other objects, advantages, and features ofthe present invention are accomplished, as embodied and fully describedherein, by a magnetic torque sensing device, which includes a generallydisk-shaped member having opposite generally circular surfaces and acentral axis of rotation; first and second magnetically conditionedregions disposed on the disk-shaped member to form a magnetoelasticallyactive region, which is both ferromagnetic and magnetorestrictive,wherein the magnetoelastically active region produces a magnetic fieldthat varies with a torque applied to the disk-shaped member, and whereinthe magnetically active region possesses sufficient magnetic anisotropyto return the magnetization in the magnetoelastically active region toan initial state when the torque applied to the disk-shaped member isreduced to zero; and at least one pair of magnetic field sensorsdisposed adjacent to one another and proximate to the magnetoelasticallyactive region, wherein sensitive directions of the magnetic fieldsensors in each pair are opposite one another and perpendicular to thedirection of polarization of the first and second magneticallyconditioned regions, wherein the magnetic field sensors provide anoutput signal that is representative of the torque applied to thedisk-shaped member, and wherein variation in the output signal issubstantially linear with respect to variation in the torque applied tothe disk-shaped member.

The magnetically conditioned regions of the device may be annularlyshaped with no gap therebetween to increase the accuracy of the torquesensing device. The device may include multiple pairs of magnetic fieldsensors to increase accuracy. The magnetic field sensors may becircumferentially oriented when magnetically conditioned regions areaxially polarized, and axially oriented when magnetically conditionedregions are circumferentially polarized to enhance the linearperformance of the device and to increase accuracy.

With those and other objects, advantages, and features of the inventionthat may become hereinafter apparent, the nature of the invention may bemore clearly understood by reference to the following detaileddescription of the invention, the appended claims and to the severaldrawings attached herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a disk-shaped member according to thepresent invention.

FIG. 2 is a side elevation view of the disk-shaped member of FIG. 1,depicting the magnetization of a magnetoelastic active region, accordingto an embodiment of the present invention.

FIG. 3 is a top plan view of the disk-shaped member of FIG. 2, depictingthe magnetization of a magnetoelastic active region, according to anembodiment of the present invention.

FIG. 4A is a graph illustrating the strengths of the magnetic fields inthe magnetically conditioned regions when the torque sensing device ofthe present invention is in a quiescent state.

FIG. 4B is a top plan view of a disk-shaped member according to thepresent invention, illustrating the relationship between the disk-shapedmember and the graph of FIG. 4A.

FIG. 5 is a top plan view of a disk-shaped member, showing illustrativepositionings of magnetic field sensors, according to another embodimentof the present invention.

FIG. 6 is a top plan view of a disk-shaped member, showing illustrativepositionings of magnetic field sensors, according to another embodimentof the present invention.

FIG. 7 is a top plan view of a disk-shaped member, showing illustrativepositionings of magnetic field sensors, according to another embodimentof the present invention.

FIG. 8 is a top plan view of a disk-shaped member, showing illustrativepositionings of magnetic field sensors, according to another embodimentof the present invention.

FIG. 9 is a top plan view of a disk-shaped member, showing illustrativepositionings of magnetic field sensors, according to another embodimentof the present invention.

FIG. 10 is a perspective view of a disk-shaped member according to thepresent invention illustrating a change in the magnetization of themagnetoelastically active region when the disk-shaped member issubjected to torque.

FIG. 11 is an exploded view showing an exemplary torque sensing deviceaccording to the present invention for use in an automotive drive train.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Several preferred embodiments of the invention are described forillustrative purposes, it being understood that the invention may beembodied in other forms not specifically shown in the drawings. Thefigures herein are provided for exemplary purposes and are not drawn toscale.

Turning first to FIG. 1, shown therein is a perspective drawing of agenerally disk-shaped member 110 in accordance with the torque sensingdevice of the present invention. The disk 110 is formed of ferromagneticmaterial and is, or at least includes, a magnetoelastically activeregion 140. The material selected for forming the disk 110 must be atleast ferromagnetic to ensure the existence of magnetic domains for atleast forming a remanent magnetization in the magnetoelastically activeregion 140, and must be magnetostrictive such that the orientation ofmagnetic field lines in the magnetoelastically active region 140 may bealtered by the stresses associated with applied torque. The disk 110 maybe completely solid, or may be partially hollow. The disk 110 may beformed of a homogeneous material or may be formed of a mixture ofmaterials. The disk 110 may be of any thickness, and is preferablybetween about 3 mm and about 1 cm thick.

The magnetoelastically active region 140 is preferably flat, andcomprises at least two radially distinct, annular, oppositely polarizedmagnetically conditioned regions 142, 144, defining themagnetoelastically active region 140 of the torque sensing device. Thetop and bottom surfaces 112, 114 do not have to be flat, however, asshown, but could have variable thickness in cross-section from thecenter of the disk 110 to the outer edge. Depending on the applicationfor which the torque sensing device is desired, it may be impractical toposition magnetic field sensors 152, 154 on both sides of the disk 110.Therefore, the present invention is designed to function in instanceswhere the magnetoelastically active region 140 is present on only onesurface of the disk 110. However, the magnetoelastically active region140 may be present on both sides of the disk 110.

FIG. 2 shows a side view of the disk 110, and illustrates a process bywhich the magnetoelastically active region 140 may be formed on anannular portion of the disk 110. As shown, two permanent magnets 202,204, having opposite directions of magnetization (and thus oppositepolarity), are positioned proximate to the surface of the disk 110 at adistance d1. Following the positioning of the permanent magnets 202,204, the disk 110 may be rotated about its central axis O, resulting inthe formation of two annular, oppositely polarized, magneticallyconditioned regions 142, 144. Alternatively, the magneticallyconditioned regions 142, 144 may be formed by rotating the permanentmagnets about the central axis O, while the disk 110 remains stationary.During creation of the magnetoelastically active region 140, the speedof rotation about the central axis O, and the distance d1 between thepermanent magnets 202, 204 and the surface of the disk 110, should bekept constant to ensure uniformity of the magnetoelastically activeregion 140 and improve the RSU performance of the torque sensing device.Preferably, during the creation of the magnetoelastically active region140, the permanent magnets 202, 204 are positioned adjacent to oneanother, with no gap therebetween, to form magnetically conditionedregions 142, 144 with no gap therebetween. The absence of a gap betweenthe magnetically conditioned regions 142, 144 is understood to result ina torque sensing device with improved RSU performance.

In forming the magnetoelastically active region 140, the strength of thepermanent magnets 202, 204, and the distance d1 between the permanentmagnets 202, 204 and the disk 110, must be carefully selected tooptimize performance of the torque sensing device. By using strongerpermanent magnets 202, 204, and by positioning permanent magnets 202,204 closer to the disk 110, one can generally produce amagnetoelastically active region 140 that will provide a stronger, moreeasily measurable signal, when employed by a torque sensing device.However, by using permanent magnets 202, 204 that are excessivelystrong, or by placing permanent magnets 202, 204 excessively close tothe disk 110, one can produce a magnetoelastically active region 140that exhibits hysteresis, which negatively affects the linearity of thesignal produced by the torque sensing device in response to an appliedtorque. Preferably, the magnetoelastically conditioned region 140 iscreated using rectangular N42 or N45 grade neodymium iron boron (NdFeB)magnets placed at a distance of between about 0.1 mm and 5 mm from thesurface of the disk 110. More preferably, magnets are placed at adistance of about 3 mm from the surface of the disk 110. Preferably, thewidth of the magnetoelastically active region 140 is not greater than 13mm. More preferably, the width of the magnetoelastically active region140 is about 10 mm.

FIG. 2 shows an embodiment having permanent magnets 202, 204 withdirections of magnetization that are perpendicular to the plane of thedisk 110. This configuration results in magnetically conditioned regions142, 144 that are initially polarized in the axial direction (i.e.,perpendicular to the disk surface). In this configuration, themagnetically conditioned regions 142, 144 are preferably polarized suchthat, in the absence of torque applied to the disk 110 (i.e., when thetorque sensing device is in the quiescent state), the magneticallyconditioned regions 142, 144 have no net magnetization components in thecircumferential or radial directions.

During formation of the magnetoelastically active region 140, thepermanent magnets 202, 204 may be positioned, as shown in FIG. 2, suchthat the innermost magnetically conditioned region 142 is created withits magnetic north pole directed upward, and the outermost magneticallyconditioned region 144 is created with its magnetic north pole directeddownward. Alternatively, during formation of the magnetoelasticallyactive region 140, the permanent magnets may be positioned such that theinnermost magnetically conditioned region 142 is created with itsmagnetic north pole directed downward, and the outermost magneticallyconditioned region 144 is created with its magnetic north pole directedupward.

FIG. 3 shows a top view of the disk 110, and illustrates an embodimentin which the magnetoelastically active region 140 is created withpermanent magnets 302, 304 having directions of magnetization that areparallel to the plane of the disk 110, in the circumferential direction.This configuration results in magnetically conditioned regions 142, 144that are initially polarized in the circumferential direction of thedisk 110. In this configuration, the magnetically conditioned regions142, 144 are preferably polarized such that, in the absence of torqueapplied to the disk 110, the magnetically conditioned regions 142, 144have no net magnetization components in the axial or radial directions.

During formation of the magnetoelastically active region 140, thepermanent magnets 302, 304 may be positioned, as shown in FIG. 3, suchthat the innermost magnetically conditioned region 142 is created withits magnetic north pole having a clockwise orientation, and theoutermost magnetically conditioned region 144 is created with itsmagnetic north pole having a counter-clockwise orientation.Alternatively, during formation of the magnetoelastically active region,the permanent magnets 302, 304 may be positioned such that the innermostmagnetically conditioned region 142 is created with its magnetic northpole having a counter-clockwise orientation, and the outermostmagnetically conditioned region 144 is created with its magnetic northpole having a clockwise orientation.

Turning to FIGS. 4A and 4B, FIG. 4A is a graph illustrating the strengthof the magnetic fields in the magnetically conditioned regions 142, 144when the torque sensing device is in the quiescent state. Values alongthe vertical axis represent the magnetic field strength of themagnetoelastically active region 140. The magnetic fields emanating fromthe surface of the disk 110 may have their principle components in theaxial direction, as with the disk 110 of FIG. 2, or in thecircumferential direction, as with the disk 110 of FIG. 3. Values alongthe horizontal axis represent distance along a radius of the disk 110from the center line O to the outer edge of the disk 110. Point Acorresponds to a point along the edge of the innermost magneticallyconditioned region 142 nearest the center of the disk 110. Point Bcorresponds to a point along the edge of the outermost magneticallyconditioned region 144 nearest the circumferential edge of the disk 110.Point C corresponds to a point along the boundary between the innermostand outermost magnetically conditioned regions 142, 144. Point r1corresponds to a point within the innermost magnetically conditionedregion 142, at which the magnetic field strength is at a maximum. Pointr2 corresponds to a point within the outermost magnetically conditionedregion 144, at which the magnetic field strength is at a maximum. FIG.4B shows the disk 110 with points A, B, C, r1, and r2 corresponding tothose points shown in the graph of FIG. 4A. Points r1 and r2,corresponding to the peak magnetic fields, indicate the distances fromthe center of the disk 110 at which magnetic field sensors 152, 154should be placed to optimize the direction of the external magneticflux, and hence maximize the performance of the torque sensing device.The units provided in FIG. 4 are for exemplary purposes and are notlimiting on the present invention.

Turning to FIG. 5, shown therein is a top plan view of the disk 110 inthe quiescent state, with a magnetoelastically active region 140 createdby permanent magnets 202, 204 as shown in FIG. 2. The magnetoelasticallyactive region 140 includes dual magnetically conditioned regions 142,144 that are oppositely polarized in positive and negative axialdirections, respectively. The dots in FIG. 5 indicate magnetic fieldlines 546 oriented perpendicular to the surface of the disk 110, suchthat the magnetic field lines 546 are directed out of the page. The X'sin FIG. 5 indicate magnetic field lines 548 oriented perpendicular tothe surface of the disk 110, such that the magnetic field lines 548 aredirected into the page.

A pair of magnetic field sensors 552, 554 is positioned proximate to themagnetoelastically active region 140, such that each magnetic fieldsensor 552, 554 is placed over the portion of the magneticallyconditioned region 142, 144 at a location where the magnetic fieldstrength is at a maximum. The magnetic field sensors 552, 554 areoriented such that their sensitive directions are perpendicular to thedirection of magnetization in the magnetoelastically active region 140.In FIG. 5, arrows indicate the sensitive directions of the magneticfield sensors 552, 554. Magnetic field sensors 552, 554 are orientedwith their sensitive directions parallel to the surface of the disk 110(i.e., in the circumferential direction), and the magneticallyconditioned regions 142, 144 are polarized perpendicular to the surfaceof the disk 110 (i.e., in the axial direction). This configurationensures that the representative signals outputted by the magnetic fieldsensors 552, 554 vary linearly with respect to variations in the torqueapplied to the disk 110.

Magnetic field sensors 552, 554 are oppositely polarized and provided inpairs. This placement technique may be referred to as a common moderejection configuration. Output signals from each of the magnetic fieldsensors 552, 554 in the pair may be summed to provide a signalrepresentative of the torque applied to the disk 110. External magneticfields have equal effects on each of the magnetic field sensors 552, 554in the pair. Because the magnetic field sensors 552, 554 in the pair areoppositely polarized, the summed output of the magnetic field sensors552, 554 is zero with respect to external magnetic fields. However,because the magnetically conditioned regions 142, 144 are oppositelypolarized, as are the magnetic field sensors 552, 554, the summed outputof the magnetic field sensors 552, 554 is double that of each individualmagnetic field sensor 552, 554 with respect to the torque applied to thedisk 110. Therefore, placing magnetic field sensors 552, 554 in a commonmode rejection configuration greatly reduces the detrimental effects ofcompassing in the torque sensing device.

Turning to the embodiment shown in FIG. 6, the disk 110 is shown in thequiescent state, and has a magnetoelastically active region 140 createdby permanent magnets 302, 304 as shown in FIG. 3. The magnetoelasticallyactive region 140 includes dual magnetically conditioned regions 142,144 that are oppositely polarized, with magnetic field lines 646, 648,in opposite circumferential directions. A pair of magnetic field sensors652, 654 may be positioned proximate to the magnetoelastically activeregion 140, such that each magnetic field sensor 652, 656 is placed overthe portion of a magnetically conditioned region 142, 144 at a locationwhere the magnetic field strength is at a maximum. The magnetic fieldsensors 652, 654 are oriented such that their sensitive directions areperpendicular to the direction of magnetization in themagnetoelastically active region 140. In FIG. 6, a dot (indicating adirection out of the page) and an X (indicating a direction into thepage) indicate the sensitive directions of the magnetic field sensors652, 654. Magnetic field sensors 652, 654 are oriented with theirsensitive directions perpendicular to the surface of the disk 110 (i.e.,in the axial direction), and magnetically conditioned regions 142, 144are polarized parallel to the surface of the disk 110 (i.e., in thecircumferential direction) to ensure that the representative signalsoutputted by the magnetic field sensors 652, 654 vary linearly withrespect to variations in the torque applied to the disk 110. Magneticfield sensors 652, 654 are placed in a common mode rejectionconfiguration to reduce the effects of compassing in the torque sensingdevice.

Turning to FIG. 7, shown therein is the disk 110 having amagnetoelastically active region 140 with dual magnetically conditionedregions 142, 144, which are polarized in opposite axial directions. Fourpairs of magnetic field sensors 552, 554 are positioned proximate to themagnetoelastically active region 140 with their sensitive directionsperpendicular to the magnetization of the magnetically conditionedregions 142, 144. The four pairs of magnetic field sensors 552, 554 areevenly spaced about the magnetoelastically active region 140 withapproximately 90 degrees between each pair. This configuration providesfor improved RSU performance because it allows for representativesignals outputted by the multiple magnetic field sensors 552, 554 to beaveraged, thereby resulting in a more accurate measurement of the torqueapplied to the disk 110. Any inaccuracies attributable to a singlemagnetic field sensor pair due to non-uniformities in themagnetoelastically active region 140 are of reduced significance whenthe representative signals from multiple magnetic field sensors 552, 554are averaged. In torque sensing devices having magnetoelastically activeregions 140 that exhibit a high degree of uniformity (i.e., RSU signalis substantially zero), as few as one pair of magnetic field sensors552, 554 may be used to achieve sufficient RSU performance. However, dueto limitations in material preparation and magnetization processes, asignificant non-zero RSU signal may be difficult to avoid. In instancesin which increased RSU performance is desired, the number of magneticfield sensor pairs may be increased. For example, eight pairs ofmagnetic field sensors 552, 554, spaced at 45 degrees, may be used.

Turning to FIG. 8, shown therein is the disk 110 having amagnetoelastically active region 140 with magnetically conditionedregions 142, 144 polarized in a single axial direction to form,essentially, a single magnetically conditioned region. A magnetic fieldsensor unit 850 includes four individual magnetic field sensors 852,854, 856, 858. Primary magnetic field sensors 852, 854 are positionedproximate to the magnetoelastically active region 140, are aligned inthe radial direction, and are similarly polarized in a directionperpendicular to the magnetization of the magnetoelastically activeregion 140. Secondary magnetic field sensors 856, 858 are positioned onopposite sides of the primary magnetic field sensors 852, 854, proximateto the disk 110, but apart from the magnetoelastically active region140, such that the secondary magnetic field sensors 856, 858 do not pickup torque induced signals. The secondary magnetic field sensors 856, 858are similarly polarized in a direction opposite that of the primarymagnetic field sensors 852, 854. This configuration may be advantageousin instances in which a noise source (not shown) creates a localmagnetic field gradient having different effects on each of the primarymagnetic field sensors 852, 854, as discussed in U.S. Pat. App. Pub. No.2009/0230953 to Lee, which is incorporated herein by reference. In suchan instance, it may be assumed that the noise source has the greatesteffect on the secondary magnetic field sensor 856, 858 closest to thenoise source, and the least effect on the secondary magnetic fieldsensor 858, 856 farthest from the noise source. It may also be assumedthat the effect of the noise source on the primary magnetic fieldsensors 852, 854 is between that of its effects on each of the secondarymagnetic field sensors 856, 858. Finally, it may be assumed that the sumof the noise induced signals picked up by the secondary magnetic fieldsensors 856, 858 is equal in value to the sum of the noise inducedsignals picked up by the primary magnetic field sensors 852, 854.Therefore, by summing the signals picked up by each of the four magneticfield sensors 852, 854, 856, 858, the effect of magnetic noise on themagnetic field sensor unit 850 is canceled, and the composite signalpicked up by the magnetic field sensor unit 850 is entirely torqueinduced.

FIG. 9 shows a configuration of the disk 110 that may be advantageous insituations in which the radial space on the disk 110 is limited. Thedisk 110 has a magnetoelastically active region 140 with a singlemagnetically conditioned region 143 polarized in a single axialdirection. A magnetic field sensor unit 950 includes four individualmagnetic field sensors 952, 954, 956, 958. Primary magnetic fieldsensors 952, 954 are positioned proximate to the magnetoelasticallyactive region 140, are aligned in the circumferential direction, and aresimilarly polarized in a direction perpendicular to the magnetization ofthe magnetoelastically active region 140. Secondary magnetic fieldsensors 956, 958 are positioned on opposite sides of the primarymagnetic field sensors 952, 954, proximate to the disk 110, but apartfrom the magnetoelastically active region 140, such that the secondarymagnetic field sensors 956, 958 do not pick up torque induced signals.The secondary magnetic field sensors 956, 958 are similarly polarized ina direction opposite that of the primary magnetic field sensors 952,954. This configuration may be advantageous in instances in which anoise source (not shown) creates a local magnetic field gradient havingdifferent effects on each of the primary magnetic field sensors 952,954, as discussed in U.S. Pat. App. Pub. No. 2009/0230953 to Lee, whichis incorporated herein by reference. In such an instance, it may beassumed that the noise source has the greatest effect on the secondarymagnetic field sensor 956, 958 closest to the noise source, and theleast effect on the secondary magnetic field sensor 958, 956 farthestfrom the noise source. It may also be assumed that the effect of thenoise source on the primary magnetic field sensors 952, 954 is betweenthat of its effects on each of the secondary magnetic field sensors 956,958. Finally, it may be assumed that the sum of the noise inducedsignals picked up by the secondary magnetic field sensors 956, 958 isequal in value to the sum of the noise induced signals picked up by theprimary magnetic field sensors 952, 954. Therefore, by summing thesignals picked up by each of the four magnetic field sensors 952, 954,956, 958, the effect of magnetic noise on the magnetic field sensor unit950 is canceled, and the composite signal picked up by the magneticfield sensor unit 950 is entirely torque induced.

FIG. 10 provides an illustration of the principle by which torqueapplied to the disk 110 is measured by the torque sensing device. Asdiscussed above, in the quiescent state, the magnetic fields in themagnetoelastically active region 140 are aligned either substantiallyexclusively in the axial direction, as shown in FIG. 5, or substantiallyexclusively in the circumferential direction, as shown in FIG. 6. Whentorque is applied to the disk 110, magnetic moments in themagnetoelastically active region 140 tend to tilt along the shear stressdirection, which forms an angle of about 45 degrees with respect to thesurface of the disk 110, as indicated by arrows A in FIG. 10. This tiltcauses the magnetization of the magnetoelastically active region 140 toexhibit a decreased component in the initial direction, and an increasedcomponent in the shear stress direction. The degree of tilt isproportional to the strength of the torque applied to the disk 110. Themagnetic field sensors 152, 154 are capable of sensing changes in thestrength of magnetic field components along the sensitive directions ofthe magnetic field sensors 152, 154. Therefore, when torque is appliedto the disk 110, magnetic field sensors 152, 154 output representativesignals that are proportional to the applied torque.

Magnetic field sensors 152, 154 are known in the art and includemagnetic field vector sensor devices such as flux-gate inductors, HallEffect sensors, and the like. Preferably, the magnetic field sensorsaccording to the present invention are flux-gate inductors having asolenoidal form. In another embodiment, the magnetic field sensors 152,154 may be integrated circuit Hall Effect sensors. Conductors 156, asshown in FIG. 10, connect the magnetic field sensors to a source ofdirect current power, and transmit the signal output of the magneticfield sensors 152, 154 to a receiving device (not shown), such as acontrol or monitoring circuit.

Turning to FIG. 11, shown therein is a perspective, exploded viewdrawing of a torque transducer 1100 in accordance with the presentinvention. In the exemplary embodiment shown, the torque transducer 1100includes a disk 1110, a hub 1120, and a shaft 1130. The disk 1110, thehub 1120, and the shaft 1130 may be, but are not necessarily, distinctelements. The disk 1110 may be an axially thin, generally disk-shapedmember, which may be completely flat or may include contours. The hub1120 functions by rigidly attaching the disk 1110 to the shaft 1130.Attachment may be accomplished, for example, directly or indirectly byany known means which permits the hub 1120 and the shaft 1130 to act asa mechanical unit such that torque applied to the shaft 1130 isproportionally transmitted to the hub 1120 and vice versa. Examples ofmeans of attachment include pins, splines, keys, welds, adhesives, pressor shrink fits, and the like. The disk 1110 may be attached to the hub1120 by any appropriate method which permits the disk 1110 and the hub1120 to act as a mechanical unit such that torque applied to the hub1120 is proportionally transmitted to the disk 1110, and vice versa.Preferably, holes 1112, 1122 are provided in the disk 1110 and the hub1120 such that holes 1112 in the disk 1110 correspond to holes 1122 inthe hub 1120. Fasteners (not shown), such as bolts, may be insertedthrough holes 1112 in the disk 1110 and corresponding holes 1122 in thehub 1120 such that a firm attachment is formed between the disk 1110 andthe hub 1120. Examples of alternative means of attachment includeriveting, welding, and the like.

The disk 1110 may be attached to a rim 1160, such that a portion of thedisk 1110 attached to the rim 1160 is radially distinct from a portionof the disk 1110 attached to the hub 1120. The rim 1160 may surround theperiphery of the disk 1110, or may be attached to a surface of the disk1110. The rim 1160 may be an integral part of the disk 1110. The disk1110 and the rim 1160 act as a mechanical unit such that torque appliedto the disk 1110 may be proportionally transmitted to the rim 1160, andvice versa. The rim 1160 may include force transfer features 1162 forthe transfer of predominately tangential forces to a driving or drivenmember.

An exemplary embodiment of the invention is a torque sensing device foruse in connection with an automobile engine wherein the disk 1110includes a drive plate, the shaft 1130 includes a crankshaft, and therim 1160 includes a torque converter. It will be apparent to thoseskilled in the art to which the invention pertains, however, that theinvention is not limited to any specific type of automobileconfiguration, nor is the invention limited to automotive applicationsin general.

The rim 1160 and the hub 1120 are preferably formed of non-ferromagneticmaterials or are magnetically isolated from the disk 1110 bynon-ferromagnetic spacers, such as low permeability rings (not shown)inserted between the hub 1120 and the disk 1110, and between the disk1110 and the rim 1160.

The magnetoelastically active region 1140 must possess sufficientanisotropy to return the magnetization to the quiescent, or initialdirection when the applied torque is reduced to zero. Magneticanisotropy may be induced by physical working of the material of thedisk 1110 or by other methods. Illustrative methods for inducingmagnetic anisotropy are disclosed in U.S. Pat. No. 5,520,059,incorporated herein by reference.

Preferably, the disk 1110 is formed from AISI 9310 material. Examples ofalternative materials from which the disk may be formed are described inU.S. Pat. Nos. 5,520,059 and 6,513,395, incorporated herein byreference. The disk 1110 may be formed of a material having aparticularly desirable crystalline structure.

In another embodiment of the present invention, the magnetoelasticallyactive region 1140 may be formed separately from the disk 1110, and thenapplied to the disk 1110 by means such as adhesives, welds, fasteners,or the like, such that torque induced in the disk 1110 is transmitted toand proportional to torque induced in the magnetoelastically activeregion 1140.

In the operation of the present invention, magnetic fields arise fromthe magnetoelastically active region 1140 and these fields pervade notonly the space in which the magnetic field sensors 1152, 1154 arelocated but also the space occupied by the disk 1110 itself.Magnetization changes that take place within non-active portions of thedisk 1110 may result in the formation of parasitic magnetic fields thatmay pervade the regions of space where the magnetic field sensors 1152,1154 are located. The hub 1120 and the rim 1160 can be formed ofnon-ferromagnetic materials to reduce or eliminate parasitic magneticfields. Thus, in the interest of not corrupting the transfer function ofthe magnetoelastically active region 1140, it is important that theparasitic fields be very small, ideally zero, in comparison with themagnetic field arising from the magnetoelastically active region or, ifof significant intensity, that they change linearly and anhysteretically(or not at all) with applied torque, and that they be stable with timeand under any of the operational and environmental conditions that theshaft 1130, the disk 1110, and the magnetoelastically active region 1140might be subjected to. Stated otherwise, any parasitic fields whicharise must be sufficiently small compared to the magnetoelasticallyactive region field such that the net field seen by the magnetic fieldsensors 1152, 1154 is useful for torque sensing purposes. Thus, in orderto minimize the corrupting influence of parasitic fields, it isimportant to utilize a disk material having a coercivity sufficientlyhigh that the field arising from the magnetoelastically active region1140 does not magnetize regions of the disk 1110 proximate to themagnetoelastically active region 1140 to give rise to such parasiticmagnetic fields which are of sufficient strength to destroy theusefulness, for torque sensing purposes, of the net magnetic field seenby the magnetic field sensors 1152, 1154. This may be accomplished, forexample, by using a material in which the coercivity of the disk 1110 isgreater than 15 Oe, preferably greater than 20 Oe, and most desirablygreater than 35 Oe.

In addition to torque, the present invention is capable of measuringpower, energy, or rotational speed, whereinPower=Torque×2π×Rotational Speed,andEnergy=Power/Time.

Although certain presently preferred embodiments of the disclosedinvention have been specifically described herein, it will be apparentto those skilled in the art to which the invention pertains thatvariations and modifications of the various embodiments shown anddescribed herein may be made without departing from the spirit and scopeof the invention. Accordingly, it is intended that the invention belimited only to the extent required by the appended claims and theapplicable rules of law.

I claim:
 1. A method of manufacturing a magnetic torque sensing devicecomprising the steps of: providing a generally disk-shaped member havingopposite generally circular spaced apart surfaces and a central axis ofrotation, wherein the disk-shaped member includes at least a portionthat is both ferromagnetic and magnetorestrictive, wherein said portionis capable of producing a magnetic field that varies with a torqueapplied to the disk-shaped member, and wherein said portion possessessufficient magnetic anisotropy to return the magnetization in saidportion to an initial state when the torque applied to the disk-shapedmember is reduced to zero; positioning a pair of oppositely polarizedpermanent magnets with no radial gap therebetween proximate to thesurface of the disk-shaped member at a first distance from a surface ofthe disk-shaped member; and rotating the disk-shaped member about itscentral axis to form two annular, oppositely polarized, magneticallyconditioned regions with no radial gap therebetween.
 2. The method, asclaimed in claim 1, wherein the permanent magnets forming the pair arearranged such that they are polarized in opposite axial directionsrelative to the disk-shaped member.
 3. The method, as claimed in claim1, wherein the permanent magnets forming the pair are arranged such thatthey are polarized in opposite circumferential directions relative tothe disk-shaped member.
 4. The method as claimed in claim 1, wherein thepermanent magnets forming the pair are rectangular N42 or N45 gradeneodymium iron boron magnets.
 5. The method, as claimed in claim 1,wherein the first distance is between about 0.1 mm and 5 mm.
 6. Themethod, as claimed in claim 1, wherein the first distance is about 3 mm.